Pentax 1.7X Teleconverter

While looking around Ebay and various forums I notice this teleconverter seems to be fetching decent money.
Just wondering how it has become so valuable, I would presume because of rarity value but have Pentax stopped making them and if so why?
Are they likely to bring out something similar (a new model perhaps)in the future for the K10D/20D etc.

When they first came out what was the recommended price compared to what they are getting now?

Thanks.

1: It's got the name Pentax on it.
2: It's a good teleconverter.
3: It AF enables MF lenses.

http://kmp.bdimitrov.de/teleconverters/F1.7X.html

it's also the only Pentax auto focus compatible teleconverter, albeit AF compatible in a somewhat bizare fashion.